Version Differences: Difficulty Setting

"Normal" mode is the same as the North American and European difficulty levels.

"Easy" mode allows you to absorb much more life and Missiles from free-floating X's and makes most of the bosses easier. Samus also doesn't take as much damage from hitting enemies.

"Hard" mode, unlocked after you beat Normal mode on that file, allows you to absorb much less life and Missiles from free-floating X's as well as limiting the amount of Energy and Missiles in Energy and Missile Tanks (50 Energy per Tank instead of 100 and 2 Missiles per Tank instead of 5, the same as Metroid Zero Mission's "Hard" mode).

The Japanese version also allows you to select between Hiragana and Kanji output (Hiragana would probably be for younger children who don't yet know enough Kanji to follow what's going on in the story).